The walls are white. Like cotton candy. What is it?

That's the alkaline substance in the wall, which is brought out by the evaporation of water in the wall. After water evaporates, the alkali in the water crystallizes to form something. This thing is called nitrate, which is a chemical raw material and an important raw material for making firecrackers. Therefore, its formation must be moisture, that is, people often say that the wall is wet or alkaline. In the construction, it is destructive, which can make the white ash fall off and the cement layer fall off in powder. Really help you look forward to adopting again.